1. Field of the Invention
This invention relates to a method and device for controlling the paper feed in a processor-driven printer.
In a general way, it applies to the printers used in man/machine dialog and to printers used for remote transcription purposes, such as printers used in Modem transmission systems or equipping telefax type devices.
It is more particularly, though not exclusively, suited to printers used in pilot/on-board computer dialog in aircraft, which are specially designed so as to be able to be manipulated in difficult conditions by a pilot sitting at the controls of his aircraft (and whose two hands are rarely available at once).
2. Description of the Prior Art
Printers of this type are known to usually comprise:
a hopper capable of containing and supporting a roll of paper while enabling it to rotate freely about an axis, PA1 a paper extraction means acting on the roll, in a region of the latter, opposite the hopper access orifice, and PA1 a guide and drive means enabling the web of paper extracted by the extraction means to be led, in succession, to a drive device, to a print station and then to an output slot possibly fitted with a paper cutting means. PA1 affixation of a mark on the web by means of a marking device situated at a first location on the path of the web, inside the printer, PA1 detection of the presence or absence of the mark at least at a second location on the path, PA1 real-time measurement of a parameter representative of the position of the mark throughout its path from the first location to the second location, PA1 comparison of the measured position with reference values defining a theoretical position of the second location, and PA1 at the instant when the measured position corresponds with the theoretical position, verification of the presence of the mark and, failing this, emission of a fault signal.
The paper feed could, of course, be synchronized with the printing tasks performed by the print head.
Usually, during the printing phase, the web of paper advances step by step, each step corresponding to a line or element of a writing line. This result is obtained by the fact that the processor which drives the print head controls the motor driving the paper feed.
Experience has shown that when the web of paper is not perforated laterally (tear strip) or when the feed is not driven by toothed wheels but by simple friction, by means of rollers, there can be occurrences of abnormal operation leading to variations in the feed speed of the paper along its path in the guide means.
This can cause printing defects such as line parallelism faults, line space variations, superimposing of lines, or even jamming phenomena putting the printer out of action.